1. Field of the Invention
This invention relates to cycloadducts formed with furan, and more particularly to the synthesis of Cantharidin.
2. Prior Art
Cantharidin is found in various species of catharides beetles, such as cantharis vesicatoria (commonly known as Spanish Fly), and has the structure ##STR1##
Notwithstanding its notoriety as a putative aphrodisiac, cantharidin has found various commercial applications, for example in the removal of benign skin growths such as warts. Cantharidin is presently commercially obtained by purification from natural sources.
Cantharidin has been an enticing but elusive target for total synthesis. Early attempts at a [4+2] cycloaddition between dimethylmaleic anhydride and furan failed, for example as reported by Otto Diels and Kurt Alder, BER., 62 (1929) 554-562. To date, there has been no commercially feasible, synthetic approach to the production of cantharidin, although three different methods for synthesis have been reported. However, these methods have involved a number of steps, have produced low yields of cantharidin, and have not proven to be commercially feasible.
Accordingly, a good and general method for synthesizing cantharidin in high yield has been lacking.